The present invention relates to a radiation tomographic imaging apparatus and method, and particularly to a radiation tomographic imaging apparatus and method for producing multi-slice tomographic images of a region through which a radiation beam having a width and a thickness passes.
Known radiation tomographic imaging apparatuses include an X-ray CT (computed tomography) apparatus, for example, that employs X-rays for the radiation. In the X-ray CT apparatus, an X-ray tube is used for the X-ray generation.
The X-ray CT apparatus is configured to rotate a radiation emitting/detecting system, i.e., an X-ray emitting/detecting system, around a subject (to scan the subject); measure projection data of the subject by the X-rays in a plurality of view directions surrounding the subject; and produce (reconstruct) a tomographic image based on the projection data.
An X-ray emitting apparatus in the X-ray emitting/detecting system emits an X-ray beam having a width that encompasses a region to be imaged and a certain thickness in a direction perpendicular to the width.
The thickness of the X-ray beam can be varied by controlling the openness of an X-ray passing opening (aperture) in a collimator, and the slice thickness for one view can thus be adjusted.
An X-ray detecting apparatus in the X-ray emitting/detecting system detects X-rays by a multi-channel X-ray detector, in which a multiplicity of (e.g. ca. 1,000) X-ray detector elements are arranged in a linear array (which will be sometimes referred to as a detector element row hereinbelow) in the width direction of the X-ray beam.
The multi-channel X-ray detector has a length (i.e., a width) equal to the width of the X-ray beam in the width direction of the X-ray beam. It also has a length (i.e., a thickness) larger than the thickness of the X-ray beam in the thickness direction of the X-ray beam.
Such multi-channel X-ray detectors include one in which, for example, a plurality of the detector element rows are arranged side by side in the thickness direction of the X-ray beam (i.e., in a direction of carrying the subject into an X-ray irradiated space (the body axis direction)) so that the plurality of detector element rows simultaneously receive the X-ray beam.
Since such an X-ray detector can obtain all the X-ray detected signals for a plurality of slices in one scan, it is used as an X-ray detector for performing a multi-slice scan with good efficiency.
In such an X-ray detector, each X-ray detector element row is configured to have a thickness (the length in the thickness direction of the X-ray beam) equal to a minimum slice thickness (e.g. 1 mm), and several to several tens, for example, of such rows are arranged side by side in the thickness direction of the X-ray beam so that the signals detected by the X-ray detector element rows can be arbitrarily combined in channels having the same index.
In the X-ray CT apparatus comprising such an X-ray detector, a multi-slice scan is performed simultaneously for three slices each having a slice thickness of 1 mm, by using the central three detector element rows, for example.
Alternatively, a multi-slice scan is performed simultaneously for three slices each having a slice thickness of 2 mm, by using the central six detector element rows to form three sets of detector element rows by combining adjacent row pairs.
Similarly, a multi-slice scan is performed simultaneously for a plurality of slices each having a different thickness, by using a number of detector element rows, the number being equal to the product of the slice thickness and the number of slices, and combining signals of a number of adjacent detector element rows, the number being equal to the slice thickness, to form a number of sets of detector element rows, the number being equal to the number of slices.
Although the conventional radiation tomographic imaging apparatus such as the X-ray CT apparatus is capable of varying the slice thickness as described above, however, the tomographic imaging is performed with the slice thickness fixed at a prespecified value during scanning, and the slice thickness cannot be dynamically switched during scanning.
Moreover, in the conventional radiation tomographic imaging apparatus, a portion near the center of the whole set of detector element rows in the X-ray detector is commonly used and portions nearer the sides are not used.
In other words, the conventional radiation tomographic imaging apparatus does not enable intentional movement of the radiation emission center in the direction of carrying the subject rested on the cradle into the radiation irradiated space (generally, in the body axis direction of the subject).
Since the slice thickness cannot be dynamically switched during scanning and the radiation emission center cannot be arbitrarily moved in the body axis direction of the subject in the radiation tomographic imaging apparatus for performing a multi-slice scan, the following disadvantage arises in performing, for example, CT fluoro (fluorography) imaging.
In order to perform the CT fluoro imaging, the subject rested on the cradle must be accurately positioned in the X-ray irradiated space, and a needle must be inserted into the subject to reach a site to be examined.
In inserting the needle, it can be confirmed by CT with certainty that the tip of the needle reached the site to be examined; however, when the position of the subject rested on the cradle is shifted due to the subject""s body motion in the conventional radiation tomographic imaging apparatus, the cradle must be moved in a direction of carrying the cradle into the X-ray irradiated space or in the opposite direction for fine adjustment of the position, and the subject may be endangered when, for example, the needle has been inserted.
The present invention was made in the light of these circumstances, and has an object to provide a radiation tomographic imaging apparatus and method in which the slice thickness can be dynamically switched during scanning, and the radiation emission center can be arbitrarily moved in a direction of carrying a subject, thereby enabling tomographic imaging with safety and high accuracy.
In order to attain such an object, a radiation tomographic imaging apparatus in a first aspect of the present invention comprises: radiation emitting means capable of emitting a radiation beam and capable of changing a range irradiated by the radiation beam in response to a control signal; a detector element array comprising a plurality of radiation detector elements with their irradiated surfaces facing in an impinging direction of the radiation beam, in which array the radiation detector elements are arranged in one of two mutually perpendicular directions to form a detector element row, and a plurality of the detector element rows are arranged side by side in the other of the two mutually perpendicular directions; control means for receiving irradiated range information and outputting the control signal to the radiation emitting means corresponding to the information; and tomographic image producing means for producing multi-slice tomographic images of a region through which the radiation beam passes based on radiation detected signals for a plurality of views detected by the detector element array corresponding to the irradiated range information.
Moreover, in the first aspect of the present invention, the radiation tomographic imaging apparatus further comprises rotating means for rotating the radiation emitting means and detector element array around a subject carried into a radiation irradiated space.
Furthermore, in the first aspect of the present invention, the radiation tomographic imaging apparatus further comprises display means for displaying the tomographic images produced by the tomographic image producing means.
A radiation tomographic imaging apparatus in a second aspect of the present invention comprises: radiation emitting means capable of emitting a radiation beam and capable of changing a range irradiated by the radiation beam in response to a first control signal; a detector element array comprising a plurality of radiation detector elements with their irradiated surfaces facing in an impinging direction of the radiation beam, in which array the radiation detector elements are arranged in one of two mutually perpendicular directions to form a detector element row, and a plurality of the detector element rows are arranged side by side in the other of the two mutually perpendicular directions; data collecting means for collecting desired data by selecting or variedly combining detected signals from the detector element rows in the detector element array in response to a second control signal; control means for receiving irradiated range information and outputting the first control signal to the radiation emitting means and the second control signal to the data collecting means corresponding to the information; and tomographic image producing means for producing multi-slice tomographic images of a region through which the radiation beam passes based on radiation detected signals for a plurality of views detected by the detector element array corresponding to the irradiated range information and collected by the data collecting means.
Moreover, in the second aspect of the present invention, the radiation tomographic imaging apparatus further comprises rotating means for rotating the radiation emitting means and detector element array around a subject carried into a radiation irradiated space.
Furthermore, in the second aspect of the present invention, the radiation tomographic imaging apparatus further comprises display means for displaying the tomographic images produced by the tomographic image producing means.
In addition, in the second aspect of the present invention, the data collecting means comprises switching means for collecting desired data by selecting or variedly combining detected signals from the detector element rows in the detector element array in response to the second control signal; and converting means for converting the data from the switching means into digital data and outputting the digital data to the tomographic image producing means.
Besides, in the second aspect of the present invention, the data collecting means comprises converting means for converting the detected signals from the detector element rows in the detector element array into digital data; and switching means for collecting desired data by selecting or variedly combining the digital data from the converting means in response to the second control signal and outputting the data to the tomographic image producing means.
A radiation tomographic imaging apparatus in a third aspect of the present invention comprises: a radiation tube for emitting radiation; a collimator capable of forming the radiation emitted by the radiation tube into a radiation beam to emit the radiation beam and capable of changing a range irradiated by the radiation beam in response to a first control signal; a detector element array comprising a plurality of radiation detector elements with their irradiated surfaces facing in an impinging direction of the radiation beam, in which array the radiation detector elements are arranged in one of two mutually perpendicular directions to form a detector element row, and a plurality of the detector element rows are arranged side by side in the other of the two mutually perpendicular directions; radiation tube moving means capable of moving an emission center of the radiation tube in the other of the two mutually perpendicular directions in response to a second control signal; control means for receiving radiation irradiated range information and outputting the first control signal to the collimator and the second control signal to the radiation tube moving means corresponding to the information; and tomographic image producing means for producing multi-slice tomographic images of a region through which the radiation beam passes based on radiation detected signals for a plurality of views detected by the detector element array corresponding to the irradiated range information.
Moreover, in the third aspect of the present invention, the radiation tomographic imaging apparatus further comprises rotating means for rotating the radiation tube, collimator and detector element array around a subject carried into a radiation irradiated space.
Furthermore, in the third aspect of the present invention, the radiation tomographic imaging apparatus further comprises display means for displaying the tomographic images produced by the tomographic image producing means.
A radiation tomographic imaging apparatus in a fourth aspect of the present invention comprises: a radiation tube for emitting radiation; a collimator capable of forming the radiation emitted by the radiation tube into a radiation beam to emit the radiation beam and capable of changing a range irradiated by the radiation beam in response to a first control signal; a detector element array comprising a plurality of radiation detector elements with their irradiated surfaces facing in an impinging direction of the radiation beam, in which array the radiation detector elements are arranged in one of two mutually perpendicular directions to form a detector element row, and a plurality of the detector element rows are arranged side by side in the other of the two mutually perpendicular directions; radiation tube moving means capable of moving an emission center of the radiation tube in the other of the two mutually perpendicular directions in response to a second control signal; data collecting means for collecting desired data by selecting or variedly combining detected signals from the detector element rows in the detector element array in response to a third control signal; control means for receiving radiation irradiated range information and outputting the first control signal to the collimator, the second control signal to the radiation tube moving means and the third control signal to the data collecting means corresponding to the information; and tomographic image producing means for producing multi-slice tomographic images of a region through which the radiation beam passes based on radiation detected signals for a plurality of views detected by the detector element array corresponding to the irradiated range information and collected by the collecting means.
Moreover, in the fourth aspect of the present invention, the radiation tomographic imaging apparatus further comprises rotating means for rotating the radiation tube, collimator and detector element array around a subject carried into a radiation irradiated space.
Furthermore, in the fourth aspect of the present invention, the radiation tomographic imaging apparatus further comprises display means for displaying the tomographic images produced by the tomographic image producing means.
In addition, in the fourth aspect of the present invention, the data collecting means comprises switching means for collecting desired data by selecting or variedly combining detected signals from the detector element rows in the detector element array in response to the third control signal; and converting means for converting the data from the switching means into digital data and outputting the digital data to the tomographic image producing means.
Besides, in the fourth aspect of the present invention, the data collecting means comprises converting means for converting the detected signals from the detector element rows in the detector element array into digital data; and switching means for collecting desired data by selecting or variedly combining the digital data from the converting means in response to the third control signal and outputting the data to the tomographic image producing means.
A radiation tomographic imaging method in a fifth aspect comprises the steps of: emitting radiation onto a first range in a detector element array comprising a plurality of radiation detector elements with their irradiated surfaces facing in an emission direction of the radiation beam, in which array the radiation detector elements are arranged in one of two mutually perpendicular directions to form a detector element row, and a plurality of the detector element rows are arranged side by side in the other of the two mutually perpendicular directions; producing multi-slice tomographic images of the first range irradiated by the radiation beam based on radiation detected signals for a plurality of views detected by the detector element array; emitting radiation onto a second range smaller than the first range in the detector element array; and producing multi-slice tomographic images of the second range irradiated by the radiation beam based on radiation detected signals for a plurality of views detected by the detector element array.
According to the present invention, irradiated range information is input via, for example, an input device, and is supplied to the control means.
The control means receives the irradiated range information, generates a control signal corresponding to the information, and outputs the control signal to the radiation emitting means.
The radiation emitting means emits a radiation beam to a desired region on the detector element array using a range corresponding to the control signal.
Then, the tomographic image producing means produces multi-slice tomographic images of a region through which the radiation beam passes based on radiation detected signals for a plurality of views detected by the detector element array corresponding to the irradiated range information. The tomographic images are displayed on, for example, the display means.
As described above, according to the present invention, the slice thickness can be dynamically switched during scanning, and the focus of the radiation can be arbitrarily moved in a direction of carrying the subject. Therefore, an advantage that tomographic imaging can be performed with safety and high accuracy can be obtained.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.